Using the Protein Data Bank, we located the protein 1OAC, otherwise known as copper amine oxidase of E. coli.  It is a dimer and has two active sites which are buried away from the solvent.  The enzyme has an inactive and an active form. 1OAC has a single copper ion and a covalently bonded cofactor.  The formation of this cofactor is done post-translationally by modifying a tyrosine side chain to 2,4,5-trihydroxyphenylalanine quinone (TPQ). (Information taken from Proteopedia)  A great summary of the enzyme is available at PDBsum.  To access that information, input the PDB code for the enzyme (1OAC).

This gallery shows two images.  The first was generated in PyMol and shows the dimer chains in two different colors.  The second image, generated by Consurf, shows the conservation of the residues of chain a (purple being most conserved, blue being most variable, and yellow representing no data available).